Boots – shoes – and leggings – Soles – Cushion
Reexamination Certificate
2000-03-16
2002-05-14
Kavanaugh, Ted (Department: 3728)
Boots, shoes, and leggings
Soles
Cushion
C036S03500R
Reexamination Certificate
active
06385864
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an improved cushioning member and method of making the same, and more particularly to a fluid filled bladder having controlled flex tensile members which allows for the formation of complex-curved contours and shapes while minimizing the amount of surrounding foam material. The present invention also relates to footwear wherein the bladder with controlled flex tensile members is used as a cushioning device within a sole.
BACKGROUND OF THE INVENTION
Considerable work has been done to improve the construction of cushioning members which utilize fluid filled bladders such as those used in shoe soles. Although with the recent developments in materials and manufacturing methods, fluid filled bladder members have greatly improved in versatility, there remain problems associated with obtaining optimum performance and durability. Fluid filled bladder members are commonly referred to as “air bladders,” and the fluid is generally a gas which is commonly referred to as “air” without intending any limitation as to the actual gas composition used.
Closed-celled foam is often used as a cushioning material in shoe soles and ethylene-vinyl acetate copolymer (EVA) foam is a common material. In many athletic shoes, the entire midsole is comprised of EVA. While EVA foam can easily be cut into desired shapes and contours, its cushioning characteristics are limited. One of the advantages of gas filled bladders is that gas as a cushioning compound is generally more energy efficient than closed-cell foam. This means that a shoe sole comprising a gas filled bladder provides superior cushioning response to loads than a shoe sole comprising only foam. Cushioning generally is improved when the cushioning component, for a given impact force, spreads the impact force over a longer period of time, resulting in a smaller impact force being transmitted to the wearer's body. Even shoe soles comprising gas filled bladders include some foam, and a reduction in the amount of foam will generally afford better cushioning characteristics.
Some major engineering problems associated with the design of air bladders formed of perimeter barrier layers include: (I) obtaining complex-curved, contoured shapes without the formation of deep peaks and valleys in the cross section which require filling in or moderating with foams or plates; (ii) ensuring that the means employed to give the air bladder its complex-curved, contoured shape does not significantly compromise the cushioning benefits of air; and (iii) reducing fatigue failure of the bladders caused by cyclic folding of portions of the bladder.
The prior art is replete with attempts to address these difficulties, but often presenting new obstacles in the process of addressing these problems. Most of the prior art discloses some type of tensile member. A tensile member is an element associated with the bladder which ensures a fixed, resting relation between the top and bottom barrier layers when the air bladder is fully inflated, and which often is in a state of tension while acting as a restraining means to maintain the general form of the bladder.
Some prior art constructions are composite structures of air bladders containing foam or fabric tensile members. One type of such composite construction prior art concerns air bladders employing an open-celled foam core as disclosed U.S. Pat. Nos. 4,874,640 and 5,235,715 to Donzis. These cushioning elements do provide latitude in their design in that the open-celled foam cores allow for complex-curved and contoured shapes of the bladder without deep peaks and valleys. However, bladders with foam core tensile members have the disadvantage of unreliable bonding of the core to the barrier layers.
FIGS. 1 and 2
illustrate a cross section of a prior art bladder
10
employing an open-celled foam core
12
as a tensile member.
FIG. 2
illustrates the loaded condition of bladder
10
with load arrows
14
. One of the main disadvantages of bladder
10
is that foam core
12
gives the bladder its shape and thus must necessarily function as a cushioning member which detracts from the superior cushioning properties of air alone. One reason for this is that in order to withstand the high inflation pressures associated with air bladders, the foam core must be of a high strength which requires the use of a higher density foam. The higher the density of the foam, the less the amount of available volume in the bladder for gas. Consequently, the reduction in the amount of gas in the bladder decreases the benefits of gas cushioning.
Even if a lower density foam is used, a significant amount of available volume is sacrificed which means that the deflection height of the bladder is reduced due to the presence of the foam, thus accelerating the effect of “bottoming out.” Bottoming out refers to the premature failure of a cushioning device to adequately decelerate an impact load. Most cushioning devices used in footwear are non-linear compression based systems, increasing in stiffness as they are loaded. Bottoming out is the point where the cushioning system is unable to compress any further. Also, the elastic foam performs a significant portion of the cushioning function and is subject to compression set. Compression set refers to the permanent compression of foam after repeated loads which greatly diminishes its cushioning aspects. In foam core bladders, compression set occurs due to the internal breakdown of cell walls under heavy cyclic compression loads such as walking or running. The walls of individual cells constituting the foam structure abrade and tear as they move against one another and fail. The breakdown of the foam exposes the wearer to greater shock forces.
Another type of composite construction prior art concerns air bladders which employ three dimensional fabric as tensile members such as those disclosed in U.S. Pat. Nos. 4,906,502 and 5,083,361 to Rudy, which are hereby incorporated by reference. The bladders described in the Rudy patents have enjoyed considerable commercial success in NIKE, Inc. brand footwear under the name Tensile-Air® and Zoom™. Bladders using fabric tensile members virtually eliminate deep peaks and valleys, and the methods described in the Rudy patents have proven to provide an excellent bond between the tensile fibers and barrier layers. In addition, the individual tensile fibers are small and deflect easily under load so that the fabric does not interfere with the cushioning properties of air.
One shortcoming of these bladders is that currently there is no known manufacturing method for making complex-curved, contoured shaped bladders using these fabric fiber tensile members. The bladders may have different heights, but the top and bottom surfaces remain flat with no contours and curves.
FIGS. 3 and 4
illustrate a cross section of a prior art bladder
20
employing a three dimensional fabric
22
as a tensile member.
FIG. 4
illustrates the loaded condition of bladder
20
with load arrows
24
. As can be seen in
FIGS. 3 and 4
, the surfaces of bladder
20
are flat with no contours or slopes.
Another disadvantage is the possibility of bottoming out. Although the fabric fibers easily deflect under load and are individually quite small, the sheer number of them necessary to maintain the shape of the bladder means that under high loads, a significant amount of the total deflection capability of the air bladder is reduced by the volume of fibers inside the bladder and the bladder can bottom out.
One of the primary problems experienced with the fabric fibers is that these bladders are initially stiffer during initial loading than conventional gas filled bladders. This results in a firmer feel at low impact loads and a stiffer “point of purchase” feel than belies their actual cushioning ability. This is because the fabric fibers have a relatively low elongation to properly hold the shape of the bladder in tension, so that the cumulative effect of thousands of these relatively inelastic fibers is a stiff effect. The tension of the outer su
Herridge David B.
Potter Daniel R.
Santos Craig E.
Sell, Jr. James C.
Kavanaugh Ted
Nike Inc.
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